Refraction-Faster then a vacuum

I was given an experiment to mesaure the refraction of light thgouh this semisircle piece of glass, (shining the light in the middle of the flat part). I measured several differnt angles of incidence and their corresponding angles of refraction.

When i graphed sin(i) to sin(r) the slope came to around 0.6, which is the index of refraction (medium 2)right? So using the equation n=c/v, my v would become greater then c, which is impossible. My slope would have to be greater then 1 for this to work.